1.Field of the Invention
This invention relates to highly insulative connectors used to secure together multiple layers of insulating and structural material within a composite wall structure. In particular, the inventive connectors secure together an insulating layer and preferably two structural layers on either side of the insulating layer. The connector rods are especially suited for construction of composite wall structures using the "tilt-up" method.
2. The Relevant Technology
As new materials and compositions have been continuously developed, novel methods for synergistically combining apparently unrelated materials to form useful composites have also been deployed. In the area of building and construction, high strength structural walls have been fabricated and then coated or layered with highly insulative materials, which generally have relatively low structural strength, to provide a composite structure having both high strength and high insulation. Conventionally, the structural component, such as a wall, is built first, after which the insulating layer or sheet is attached to the structural component. Thereafter a protective cover is placed over the insulating material to protect and hide it. The purpose of the insulation barrier is to impede the transfer of thermal energy across the structural wall.
One of the least expensive and strongest building materials that has found extensive use in the construction industry is concrete, which is typically formed from a mixture of hydraulic cement, water, and an aggregate, including rocks, pebbles and sand. Unfortunately, concrete has the drawback of offering relatively poor insulation compared to highly insulating materials such as fiberglass or polymeric foam materials. While an 8 inch slab of concrete has an R value (or thermal resistance) of 0.64, a 1 inch panel of polystyrene foam has an R value of 5.0. Conversely, highly insulative materials, at least those of reasonable cost, typically offer little in terms of structural strength or integrity. Though lightweight aggregates having higher insulating ability may be incorporated within concrete to increase the insulating effect of the concrete, the use of perlite in an amount that has a dramatic effect on the insulation ability of the concrete will usually result in greatly decreased strength of the resulting structure.
While structural walls made of cement or masonry can be fitted or retrofitted with any number of insulating materials, including insulating mats or sheets that are attached to the inner wall, or foams that are sprayed between an inner and outer wall, one strategy has been to manufacture a composite wall structure having two structural layers separated by a core insulating layer. However, in order for the two-structural-layer wall to have sufficient strength and integrity, and to prevent the two structural walls from collapsing together or separating apart during construction and subsequent use of the building, it is necessary to structurally bridge the two structural walls together. This has usually been accomplished through the use of metal studs, bolts, or beams.
However, because metal is very conductive (i.e., has very low thermal resistance), such studs, bolts, beams, or other means for structurally bridging the two walls together can also create a heat conduit or conductive thermal bridge across which heat can readily flow, notwithstanding their being surrounded by ample amounts of an insulating material. As a result, heat can rapidly flow from a relatively warm inside wall to a colder outside wall during cold weather, for example. Therefore, though the structural walls might be separated by a very efficient insulating material having a high R value (which is the measure of the resistance to flow of thermal energy, or heat, across the material), the net R value of the overall composite structure will often be far less when metal or other noninsulating connectors are used, thus negating or at least greatly diminishing the effect of the insulation layer. Of course, one might construct a building having no structural supports or connectors between the inner and outer walls; however, the result will be a wall having inadequate strength for most building needs.
Examples of composite wall structures using metal tie rods or studs may be found in the following U.S. patents: U.S. Pat. No. 4,393,635 to Long, U.S. Pat. No. 4,329,821 to Long et al., U.S. Pat. No. 2,775,018 to McLaughlin, U.S. Pat. No. 2,645,929 to Jones, and U.S. Pat. No. 2,412,744 to Nelson. As stated above, the composite wall structures disclosed in these references have a substantially lower R value than that of the highly insulating layer due to the thermal bridging effect of the highly conductive metal studs or connectors that pass through the cross section of the insulating layer.
In order to minimize the problem of thermal bridging, some have employed connector rods having a metal portion that passes through the concrete layers and a thermally insulating portion that passes through the insulating layer (e.g., U.S. Pat. No. 4,545,163 to Asselin). Others have developed connector rods made entirely from high R-value materials. For example, U.S. Pat. No. 4,829,733 to Long (hereinafter the "Long '733 Patent") discloses a plastic shear connector used in forming an insulated wall having an inner and an outer concrete structural layer, with a highly insulating layer sandwiched therebetween. Although the plastic shear connector described in the Long '733 Patent has found some use in the construction industry, the design of the connector described therein, together with the method for making such a connector, create added materials, manufacturing, and labor costs due to the relatively inefficient method of forming and then using the connector set forth in the Long '733 Patent. A summary of the method used to manufacture the preferred connector rods disclosed in the Long '733 Patent, as well as a summary of the limitations in their use and effectiveness, are set forth in copending U.S. application Ser. No. 08/255,910, filed Apr. 8, 1994, and issued as U.S. Pat. No. 5,519,973 (hereinafter the "'973 Patent"), which has been incorporated by specific reference for disclosure purposes.
One method for manufacturing the composite wall structure described herein is the so-called "tilt-up" method, whose manufacture is described hereinbelow. Examples of useful connector rods used in the tilt-up method may be found in the '973 Patent, which connectors have a substantially pointed tip at one end and an enlarged head at the other. Both aid in the placement of the connector rods compared to, e.g., the connector disclosed in the Long '733 Patent. The tilt-up method for manufacturing composite wall structures is typically carried out as follows.
First, concrete is poured into a horizontally configured form to form a first unhardened structural layer. Second, the insulating layer is placed over the surface of the still uncured first structural layer. Third, the connector rods are inserted through the exposed horizontal surface of the insulating layer so that a first portion of the connector rods extends into the interior of the uncured first structural layer, so that a second portion spans the width of the insulating layer, and so that a third portion extends outwardly from the insulating layer surface. The connector rods are preferably twisted in order to consolidate the uncured concrete into a locking structure or recess within the first portion of the connector rod to ensure eventual secure anchoring of the connector rod within the first horizontal slab. Fourth, either before or after substantial hardening of the first structural layer, a second concrete layer is poured over the surface of the insulating layer within a form in order to form the second structural layer. The third portion of the connector rods is preferably fully enveloped within the second structural layer. Fifth, after the first and second structural layers have been adequately cured and the forms removed, the horizontally positioned composite wall structure is tilted up vertically by means of a hoist or crane and positioned into the desired location.
A second method for manufacturing the composite wall structure is the "cast-in-place" method, wherein the structural walls are poured within a vertical form that has been built in a location at or near where the composite wall structure is to be finally located. In the cast-in-place method, connector rods having a length corresponding to the width of the entire composite wall structure are placed substantially orthoginally through the insulating layer, with a first portion extending out of one surface of the insulating layer, a second portion extending through the width of the insulating layer, and a third portion extending out the other surface of the insulating layer.
The insulating layer with the connector rods extending out of both surfaces is then placed parallel to and between the walls of the form. The extended portions of the connector rods horizontally span the form and maintain the insulating layer in a properly spaced arrangement between the two walls of the form, with vertical spaces between each side of the insulating layer and the form walls where the structural material is to be poured. Thereafter, concrete or other hardenable structural material is poured within each of the two vertical spaces to form a structural layer on either side of the insulating layer. Upon curing and removal of the form, the structural layers and insulating layer are locked together by means of the connector rods to form the composite wall structure. Examples of connector rods used in the cast-in-place method may be found in U.S. application Ser. No. 08/558,734 referenced above (hereinafter the "'734 Application").
In light of the foregoing, what are needed are improved insulating connectors and methods for manufacturing highly insulative composite wall structures.
In addition, what are needed are improved designs and methods for molding improved insulating connectors in a single step that yet provide adequate strength and support in the manufacture of composite wall structures.
Additionally, it would be an improvement in the art to provide improved connectors that can be molded in a single step and yet provide means for anchoring the connectors within the concrete layers while also providing means for positioning the connectors within the insulating layer during the formation of the composite wall structure.
In addition, it would be an improvement in the art to provide connectors that can be integrally molded in one step without the need to separately mold an elongate connector shaft having means for retaining the shaft within the outer structural layers and a central sleeve portion having a flange and an enlarged central diameter for positioning the connector within the insulating layer.
It would be a further improvement in the art to provide improved connectors having means for facilitating their penetration through an insulating layer and a first of two structural layers during the formation of a composite wall structure, particularly using the tilt-up method.
Finally, it would be a tremendous advancement in the art to provide improved connectors having means for receiving an impact, such as from a hammer or a mallet and/or features which aid in gripping the connector in order to facilitate penetration of the connectors through the insulating layer and the first structural layer. Such improved connectors having improved design features and methods for manufacturing such connectors having the aforesaid design features are set forth and claimed herein.